feat(04-01): install new deps + scaffold API test harness with Wave-0 RED stubs

- Add react-router@7, @dnd-kit/core, @dnd-kit/sortable, fractional-indexing to PWA
- Add fractional-indexing to API (rank generation server-side)
- ioredis NOT added (in-memory EventEmitter per RESEARCH Plan 02 justification)
- Create apps/api/test/setup.ts with afterEach DB cleanup for list tables
- Wire test.setupFiles in apps/api/vitest.config.ts
- Add 4 Wave-0 RED stub test files (LIST-01/02/03/04, D-04, D-11, D-07)
- All stubs run as todo, not import-error

apps/pwa/src/hooks/useListSSE.test.ts

@@ -0,0 +1,20 @@
+/**
+ * Wave-0 RED stubs for useListSSE hook.
+ *
+ * Covers D-11: bounded (capped exponential) backoff before showing the
+ * "disconnected / updates paused" indicator.
+ *
+ * Tests use a mock EventSource that simulates connect/disconnect scenarios.
+ * Downstream plans implement the actual useListSSE.ts hook.
+ *
+ * Run: pnpm --filter @familysync/pwa test
+ */
+
+describe('useListSSE — D-11 bounded backoff', () => {
+  it.todo('starts connected when EventSource fires the open event')
+  it.todo('attempts to reconnect with exponential backoff on error')
+  it.todo('stops retrying after the configured max attempts and sets status to disconnected')
+  it.todo('resets backoff counter on successful reconnect')
+  it.todo('calls onMessage callback with parsed event data when a message arrives')
+  it.todo('cleans up EventSource on unmount')
+})